(Received: September 27, 2011)
(Accepted for publication: December 7, 2011)

Abstract:
Decline of larch trees has been recently observed in eastern Siberia. We hypothesized that the decline might be caused by changes in soil water conditions of larch forests, especially wetting tendency due to recent climate change. Through pot experiments, we have investigated the effects of wet or dry soil water conditions on growth and abscission of roots in two larch species viz. Larix gmelinii that grows in boreal forests and Larix leptolepis that grows in temperate regions. The results showed that both the allocation of photosynthetic products to roots and the activity of roots decrease under wet conditions compared with drought conditions in L. gmelinii. However, the opposite results were obtained in L. leptolepis. The root response of L. gmelinii to wet conditions may be one of the causes of the recent decline in Siberian larch forests under elevated soil water conditions.